One who's been caught arriving with drugs in need of support (8)
I believe the answer is:
arrestee
'one who's been caught' is the definition.
(someone who's been arrested)
'arriving with drugs in need of support' is the wordplay.
'arriving' becomes 'arr' (abbreviation used in transport).
'with' is a charade indicator (letters next to each other).
'drugs' becomes 'es' (ecstasy tablets).
'in need of' is a charade indicator (letters next to each other).
'support' becomes 'tee' (tee is a kind of support).
'arr'+'es'+'tee'='ARRESTEE'
(Other definitions for arrestee that I've seen before include "One run in by the police" , "one's suspected?" , "American criminal perhaps" , "Person seized by legal authority" , "one bust" .)